1. Field of the Invention
The present invention relates to a gas turbine starting method, which includes to reduce an air amount to be discharged into the air and to avoid a fluid unstableness phenomenon occurring in a compressor both at the time of starting.
2. Description of the Prior Art
FIG. 3 is a cross sectional view of one example of a gas turbine compressor in the prior art. In FIG. 3, numeral 50 designates a compressor and numeral 10 designates a rotor. The rotor 10 has rotor vanes M1, M2, M3, M4, . . . (illustration shows an example of 10 stages) fitted to an outer circumferential periphery of a rotor disc so as to be rotated together with the rotor 10. On the other hand, stator vanes C1, C2, C3, C4, . . . are fitted to an inner circumferential wall of a casing 14 so that the stator vanes and the rotor vanes are arranged alternately in an axial direction of the compressor 50.
At an inlet of the compressor 50, an IGV (Inlet Guide Vane) 11 is fitted to the inner circumferential wall of the casing 14 so as to adjustable of its opening by a driver portion 12.
Of the stator vanes shown in the example of FIG. 3, those of C1, C2, C3 and C4 are variable vanes and their openings are adjustable by respective driver portions 13-1, 13-2, 13-3 and 13-4. Air 20 is adjusted of a flow rate by the opening of the IGV 11 to enter the compressor 50 to be compressed while flowing through between the respective stator vanes and between the rotating rotor vanes and a compressed air 21 flows out of the compressor 50 to be supplied as a gas turbine combustion air or a turbine rotor or turbine blade cooling air. It is to be noted that while description is made with respect to FIG. 3 on the example of the compressor 50 having the vanes of 10 stages in total in which four stages of the stator vanes C1, C2, C3 and C4 are variable, such a compressor as having vanes of 15 stages in total in which five stages of stator vanes C1 to C5 are variable is also developed.
FIG. 4 is a diagrammatic constructional view of stator vanes and their surrounding portion of the above-mentioned compressor in the prior art having five stages of variable stator vanes C1 to C5. In FIG. 4, an IGV 11 is provided at an inlet of a compressor 50 and stator vanes C1 to C15 are arranged, although not all the stator vanes are illustrated. An opening 15 is provided immediately after the fifth stage stator vane C5 so as to communicate with a piping 30. The piping 30 is provided at its middle way with a bleed valve 60 for bleeding a compressed air. Likewise, an opening 16 is provided immediately after the eighth stage stator vane C8, and a piping 31 and a bleed valve 61 communicate therewith. Also, an opening 17 is provided immediately after the eleventh stage stator vane C11, and a piping 32 and a bleed valve 62 communicate therewith. It is to be noted that the openings 15, 16, 17, respectively, are provided at four places on an outer circumferential periphery of a casing and four pipings each of the pipings 30, 31, 32 join together to communicate with the respective bleed valves 60, 61, 62.
In the gas turbine compressor constructed as above, while the IGV 11 and the five stages of the stator vanes C1 to C5 are adjustable of their openings, the bleed valves 60, 61, 62 are so constructed as to be either fully opened or fully closed by an ON/OFF operation. At the time of starting, the IGV 11 and the stator vanes C1 to C5 are set to a predetermined opening, the bleed valves 60, 61, 62 are fully opened and air 20 is compressed. Until a rise of the gas turbine, the compressor is operated by a drive of a starter motor. At an initial slow speed operation and until the speed is elevated to about 90%, the bleed valves 60, 61, 62 are fully opened so that the air 20 is bled to be discharged into the ambient air for a matching of an air flow rate to the slow speed operation. When the speed comes to 90% of a rated speed and the operation rises up, the bleed valves 60, 61, 62 are fully closed and a steady operation starts. In such circumferences, there are problems in the prior art that a mismatching of the air flow rate occurs at the initial stage of the starting or a flow rate unstableness phenomenon occurs at the time when the bleed valves are closed while the speed is being elevated, etc. as well as the starter motor must have a large capacity in order to ensure a starting force at the time of operation start.
In the prior art gas turbine compressor, as mentioned above, when the operation is started, the starter motor is driven and the bleed valves are fully opened so that air is bled on the way for a matching to the operation state and when the speed is elevated to about 90%, the bleed valves are fully closed and the steady operation starts. In the mentioned operation method, while the speed is being elevated from the starting, a large amount of the air compressed halfway is discharged in vain into the ambient air.
Further, the starter motor is needed to have a sufficient capacity taking account of the air flow rate to be discharged into the ambient air at the time of starting. Also, the adjustment of the bleed valves to meet the air flow rate of the initial slow speed operation time and that of the compressor rated operation time is only done by the ON/OFF operation by which the bleed valves are either fully opened or fully closed, hence a phenomenon to cause an unstable fluid flow occurs at the starting time, which results in the obstruction in achieving a smooth speed elevation.